Remote rf power system with low profile transmitting antenna

ABSTRACT

An antenna assembly includes: an antenna including: a metal signal layer having a radiating surface; and a feed port; and a waveguide surrounding the antenna and configured to guide electromagnetic energy transmitted from the radiating surface in a direction away from the antenna; and a controller module connected to the feed port and configured to drive the antenna to transmit electromagnetic energy from the radiating surface; wherein the antenna, waveguide, and controller module are configured such that, when the controller module drives the antenna, the transmitted electromagnetic energy matches a reception characteristic of an implantable device and is sufficient for the implantable device to create one or more electrical pulses of sufficient amplitude to stimulate neural tissue of a patient, solely using electromagnetic energy received from the antenna, when the implantable device is located at least 10 centimeters away from the antenna.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation (and claims the benefit of priorityunder 35 USC 120) of U.S. application Ser. No. 14/710,548, filed May 12,2015, now allowed, which claims the benefit of U.S. ProvisionalApplication Ser. No. 61/992,150, filed May 12, 2014. Both of these priorapplications are incorporated by reference in their entirety.

TECHNICAL FIELD

This application generally relates to a RF stimulation system includingan antenna assembly to remotely provide power and stimulation parametersto an implantable device.

BACKGROUND

Antennas have been designed and utilized with implanted devices to aidin the treatment of various medical conditions. Often, these antennasare placed close to the patient's body. In some cases, the conductiveelement of the antennas would be subject to excessive absorption ofelectromagnetic energy, which, when these antennas are placed close tothe patient's body, could lead to adverse events such as burning oftissue, creation of undesirable blood clots and skin irritation fromadherence of the antenna directly to skin tissue.

SUMMARY

In one aspect, some implementations provide antenna assembly, including:an antenna that includes: a metal signal layer having a radiatingsurface; and a feed port; and a waveguide surrounding the antenna andconfigured to guide electromagnetic energy transmitted from theradiating surface in a direction away from the antenna; and a controllermodule connected to the feed port and configured to drive the antenna totransmit electromagnetic energy from the radiating surface; wherein theantenna, waveguide, and controller module are configured such that, whenthe controller module drives the antenna, the transmittedelectromagnetic energy matches a reception characteristic of animplantable device and is sufficient for the implantable device tocreate one or more electrical pulses of sufficient amplitude tostimulate neural tissue of a patient, solely using electromagneticenergy received from the antenna, when the implantable device is locatedat least 10 centimeters away from the antenna.

Implementations may include one or more of the following features. Theantenna assembly may further include a dielectric lens that fills thewave guide and protrude outward from an opening of the wave guide toform a protrusion that is shaped to spatially narrow the transmittedelectromagnetic energy in the direction away from the transmittingsurface. The protrusion may be tapered in shape. The protrusion may betapered to have a Gaussian or sinusoid profile.

The antenna assembly may have a return loss cutoff frequency associatedwith the wave guide and the dielectric lens may be further configured tolower the return loss cutoff frequency. The antenna may be operablewithin a frequency band from about 500 MHz to about 4 GHz. The radiatingsurface may be bowtie shaped and has two leaf structures connecting toeach other at the feed port as well as through two substantiallyparallel rod structures. The transmitted electromagnetic energy may bepolarized along a long axis of the rod structures. The radiating surfacemay be adjustable from a first spatial orientation to a second spatialorientation such that polarized electromagnetic energy received at theimplantable device is increased.

The waveguide may be a rectangular waveguide having four walls thatsurround the bowtie shaped radiating surface. The rectangular waveguidemay have an interior length of about 15 cm, an interior width of about7.6 cm, and a height of about 5 cm. The rectangular waveguide may havean interior length of at least 10 cm, and the rectangular waveguide mayhave an interior length, width, and height ratio of about 15:7.6:5.

In another aspect, some implementations may include a method forwirelessly supplying energy to an implantable device, the methodincluding: radiating electromagnetic energy from a radiating surface onan antenna assembly, the radiated electromagnetic energy reaching animplantable device located at least 10 centimeters away and implantedinside a patient such that the implantable device creates, solely byusing the radiated electromagnetic energy, one or more electricalstimulation pulses suitable for stimulating neural tissue of thepatient, and applies the electrical stimulation pulses to neural tissueof the patient.

Implementations may include one or more of the following features.Radiating the electromagnetic energy may further include radiating theelectromagnetic energy while the patient is asleep such that the createdone or more electrical simulation pulses is applied to stimulate thepatient's neural tissue during the patient's sleep.

The method may further include: adjusting a position of the antennaassembly such that the radiating surface of the antenna assembly is nomore than six feet from the implantable device. The method may furtherinclude: adjusting a position of the antenna assembly such that theradiating surface of the antenna assembly is no less than one foot fromthe implantable device. The method may further include: adjusting anorientation of the antenna assembly such that the radiatedelectromagnetic energy received at the implantable device is increased.The method may further include: connecting the antenna assembly to acontroller module; and driving the antenna assembly from the controllermodule connected thereto such that the radiating surface on the antennaassembly radiates electromagnetic energy to power the implantable. Themethod may further include establishing a link between a programmingmodule to the controller module; and transmitting, from the programmingmodule to the controller module, data encoding parameters of the one ormore stimulation pulses to be created at the implantable device and tobe subsequently applied to stimulate the patient's neural tissue.

In yet another aspect, some implementations may include a system thatincludes: an antenna assembly that wirelessly powers an implantabledevice, the antenna assembly including: an antenna that includes: ametal signal layer having a radiating surface and configured to transmitelectromagnetic energy via radiative coupling; a waveguide surroundingthe antenna and configured to guide electromagnetic energy transmittedfrom the radiating surface in a direction away from the antenna; and; acontroller module connected to the feed port of the antenna andconfigured to drive the antenna assembly such that the radiating surfaceon the antenna radiates electromagnetic energy.

Implementations may include one or more of the following features. Thesystem may further include an implantable operable from a locationinside a patient and more than 10 centimeters away from the antennaassembly, wherein the implantable device creates one or more stimulationpulses of sufficient amplitude to stimulate neural tissue of the patientsolely using electromagnetic energy received from the antenna assembly.

The waveguide may be a rectangular waveguide having four walls thatsurround the radiating surface. The rectangular waveguide may have aninterior length of about 15 cm, an interior width of about 7.6 cm, and aheight of about 5 cm. The rectangular waveguide may have an interiorlength of at least 10 cm, and the rectangular waveguide may have aninterior length, width, and height ratio of about 15:7.6:5.

The system may further include a dielectric lens that fills the waveguide and protrude outward from an opening of the wave guide to form aprotrusion that is shaped to spatially narrow the transmittedelectromagnetic energy in the direction away from the transmittingsurface. The protrusion may be tapered in shape. The protrusion may betapered to have a Gaussian or sinusoid profile.

The antenna may be operable within a frequency band from about 500 MHzto about 4 GHz. The radiating surface may be bowtie shaped and has twoleaf structures connecting to each other at the feed port as well asthrough two substantially parallel rod structures.

The transmitted electromagnetic energy may be polarized along a longaxis of the rod structures. The implantable device may include a dipoleantenna located on the implantable device inside the patient, and theradiating surface is adjustable from a first spatial orientation to asecond spatial orientation such that polarized electromagnetic energyreceived at the dipole antenna is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a high-level diagram of an example of a wirelessstimulation system.

FIG. 2 depicts a detailed diagram of an example of the wirelessstimulation system.

FIGS. 3A-3C show examples of operations of a microwave stimulationsystem.

FIGS. 4A-4B show examples of radiation volumes when the microwavestimulation system is in operation.

FIGS. 5A-5B show an example of an antenna assembly of the wirelessstimulation system.

FIGS. 6A-6C are illustrations of an antenna assembly with a wave guide.

FIG. 7 shows an example of the return loss characteristics of theantenna assembly of FIGS. 6A-6C.

FIG. 8 shows an example of simulated return loss characteristics of anantenna assembly with a resonance at about 915 MHz.

FIGS. 9A-9B show examples of simulated electromagnetic radiationpatterns from the antenna assembly of FIG. 8.

FIG. 10 illustrates an example of an antenna assembly including abowtie-shaped radiating surface, a wave guide, and a dielectric lens.

FIGS. 11A-11B shows the simulated return loss and transmissioncharacteristics of the antenna assembly of FIG. 10.

FIG. 12 shows the perspective view of the simulated electromagneticradiation pattern from the antenna assembly of FIG. 10.

FIG. 13A-13B shows the X-Z and Y-Z plane view of the simulatedelectromagnetic radiation pattern of FIG. 12.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In various implementations, systems and methods are disclosed forapplying one or more electrical impulses to targeted excitable tissue,such as nerves, for treating chronic pain, inflammation, arthritis,sleep apnea, seizures, incontinence, pain associated with cancer,incontinence, problems of movement initiation and control, involuntarymovements, vascular insufficiency, heart arrhythmias, obesity, diabetes,craniofacial pain, such as migraines or cluster headaches, and otherdisorders. In certain embodiments, a device may be used to sendelectrical energy to targeted nerve tissue by using remote radiofrequency (RF) energy without cables or inductive coupling to power apassive implanted wireless stimulator device. The targeted nerves caninclude, but are not limited to, the spinal cord and surrounding areas,including the dorsal horn, dorsal root ganglion, the exiting nerveroots, nerve ganglions, the dorsal column fibers and the peripheralnerve bundles leaving the dorsal column and brain, such as the vagus,occipital, trigeminal, hypoglossal, sacral, coccygeal nerves and thelike.

A wireless stimulation system can include an implantable stimulatordevice with one or more electrodes and one or more conductive antennas(for example, dipole or patch antennas), and internal circuitry forfrequency waveform and electrical energy rectification. The system mayfurther comprise an external controller and antenna for transmittingradio frequency or microwave energy from an external source to theimplantable stimulator device with neither cables nor inductive couplingto provide power.

In various implementations, the wireless implantable stimulator deviceis powered wirelessly (and therefore does not require a wiredconnection) and contains the circuitry necessary to receive the pulseinstructions from a source external to the body. For example, variousembodiments employ internal dipole (or other) antenna configuration(s)to receive RF power through electrical radiative coupling. This allowssuch devices to produce electrical currents capable of stimulating nervebundles without a physical connection to an implantable pulse generator(IPG) or use of an inductive coil.

Antennas can be designed for the purpose of transmitting microwaveenergy to a receiving antenna located just below a patient's skin, or onthe skin, from a distant location (e.g., of up to four to six feet andstationary). The antenna design may be dependent on the mobility needsof the patient while receiving the therapy. The antenna mayadvantageously have a minimum profile so that the antenna can blend inwith the ambiance of the room. The disclosure focuses on the design of acompact remote transmitting antenna with superior matching and gain, aswell as being several orders of magnitude less expensive than comparableantennas and very easy to manufacture.

According to some implementations, a wireless stimulation system caninclude an antenna assembly coupled to a controller module andconfigured to radiate electromagnetic energy to an implantable device.In some instances, the implantable device can be a passive neuralstimulator device configured to receive RF energy and stimulationparameters wirelessly. Solely by using the received electromagneticenergy, the implantable passive neural stimulator creates one or morestimulation pulses to stimulate neural tissue of a patient. Inparticular, the antenna assembly can include an antenna with abowtie-shaped radiating surface and a feed port. The feed port may becoupled to a controller module that drives the antenna to transmit theelectromagnetic energy from the bowtie radiating surface. The bowtieshaped radiating surface is generally sized and shaped to radiate theelectromagnetic energy to match a reception characteristic of theimplantable passive neural stimulator. In one example, the implantablepassive neural stimulator includes a dipole antenna and the radiatingsurface is configured to transmit polarized electromagnetic energycommensurate with dipole reception characteristics. Moreover, theantenna assembly may further include a wave guide that surrounds theantenna to direct the transmitted electromagnetic energy away from theradiating surface. In some instances, a dielectric lens fills thewaveguide and extend outward from an opening of the wave guide to form aprotrusion. The protrusion is shaped to spatially narrow the transmittedelectromagnetic energy in the direction away from the transmittingsurface. The protrusion may be tapered in shape and may have a Gaussianor sinusoid profile.

Further descriptions of exemplary wireless systems for providing neuralstimulation to a patient can be found in commonly-assigned, co-pendingpublished PCT applications PCT/US2012/23029 filed Jan. 28, 2011,PCT/US2012/32200 filed Apr. 11, 2011, PCT/US2012/48903, filed Jan. 28,2011, PCT/US2012/50633, filed Aug. 12, 2011 and PCT/US2012/55746, filedSep. 15, 2011, the complete disclosures of which are incorporated byreference.

FIG. 1 depicts a high-level diagram of an example of a wirelessstimulation system. The wireless stimulation system may include fourmajor components, namely, a programmer module 102, a RF pulse generatormodule 106, a transmit (TX) antenna 110 (for example, a patch antenna,slot antenna, or a dipole antenna), and an implanted wireless stimulatordevice 114. The programmer module 102 may be a computer device, such asa smart phone, running a software application that supports a wirelessconnection 104, such as Bluetooth®. The application can enable the userto view the system status and diagnostics, change various parameters,increase/decrease the desired stimulus amplitude of the electrodepulses, and adjust feedback sensitivity of the RF pulse generator module106, among other functions.

The RF pulse generator module 106 may include communication electronicsthat support the wireless connection 104, the stimulation circuitry, andthe battery to power the generator electronics. In some implementations,the RF pulse generator module 106 includes the TX antenna embedded intoits packaging form factor while, in other implementations, the TXantenna is connected to the RF pulse generator module 106 through awired connection 108 or a wireless connection (not shown). The TXantenna 110 may be coupled directly to tissue to create an electricfield that powers the implanted wireless stimulator device 114. The TXantenna 110 communicates with the implanted wireless stimulator device114 through an RF interface. For instance, the TX antenna 110 radiatesan RF transmission signal that is modulated and encoded by the RF pulsegenerator module 110. The implanted wireless stimulator device of module114 contains one or more antennas, such as dipole antenna(s), to receiveand transmit through RF interface 112. In particular, the couplingmechanism between antenna 110 and the one or more antennas on theimplanted wireless stimulation device of module 114 utilizes electricalradiative coupling and not inductive coupling. In other words, thecoupling is through an electric field rather than a magnetic field.

Through this electrical radiative coupling, the TX antenna 110 canprovide an input signal to the implanted wireless stimulator device 114.This input signal contains energy and may contain information encodingstimulus waveforms to be applied at the electrodes of the implantedwireless stimulator device 114. In some implementations, the power levelof this input signal directly determines an applied amplitude (forexample, power, current, or voltage) of the one or more electricalpulses created using the electrical energy contained in the inputsignal. Within the implanted wireless stimulator device 114 arecomponents for demodulating the RF transmission signal, and electrodesto deliver the stimulation to surrounding neuronal tissue.

The RF pulse generator module 106 can be implanted subcutaneously, or itcan be worn external to the body. When external to the body, the RFgenerator module 106 can be incorporated into a belt or harness designto allow for electric radiative coupling through the skin and underlyingtissue to transfer power and/or control parameters to the implantedwireless stimulator device 114. In either event, receiver circuit(s)internal to the wireless stimulator device 114 (or cylindrical wirelessimplantable stimulator device 1400 shown in FIGS. 14A and 14B, helicalwireless implantable stimulator device 1900 shown in FIGS. 19A to 19C)can capture the energy radiated by the TX antenna 110 and convert thisenergy to an electrical waveform. The receiver circuit(s) may furthermodify the waveform to create an electrical pulse suitable for thestimulation of neural tissue.

In some implementations, the RF pulse generator module 106 can remotelycontrol the stimulus parameters (that is, the parameters of theelectrical pulses applied to the neural tissue) and monitor feedbackfrom the wireless stimulator device 114 based on RF signals receivedfrom the implanted wireless stimulator device 114. A feedback detectionalgorithm implemented by the RF pulse generator module 106 can monitordata sent wirelessly from the implanted wireless stimulator device 114,including information about the energy that the implanted wirelessstimulator device 114 is receiving from the RF pulse generator andinformation about the stimulus waveform being delivered to the electrodepads. In order to provide an effective therapy for a given medicalcondition, the system can be tuned to provide the optimal amount ofexcitation or inhibition to the nerve fibers by electrical stimulation.A closed loop feedback control method can be used in which the outputsignals from the implanted wireless stimulator device 114 are monitoredand used to determine the appropriate level of neural stimulationcurrent for maintaining effective neuronal activation, or, in somecases, the patient can manually adjust the output signals in an openloop control method.

FIG. 2 depicts a detailed diagram of an example of the wirelessstimulation system. As depicted, the programming module 102 may compriseuser input system 202 and communication subsystem 208. The user inputsystem 221 may allow various parameter settings to be adjusted (in somecases, in an open loop fashion) by the user in the form of instructionsets. The communication subsystem 208 may transmit these instructionsets (and other information) via the wireless connection 104, such asBluetooth or Wi-Fi, to the RF pulse generator module 106, as well asreceive data from module 106.

For instance, the programmer module 102, which can be utilized formultiple users, such as a patient's control unit or clinician'sprogrammer unit, can be used to send stimulation parameters to the RFpulse generator module 106. The stimulation parameters that can becontrolled may include pulse amplitude, pulse frequency, and pulse widthin the ranges shown in Table 1. In this context the term pulse refers tothe phase of the waveform that directly produces stimulation of thetissue; the parameters of the charge-balancing phase (described below)can similarly be controlled. The patient and/or the clinician can alsooptionally control overall duration and pattern of treatment.

Stimulation Parameter Table 1 Pulse Amplitude: 0 to 20 mA PulseFrequency: 0 to 10000 Hz Pulse Width: 0 to 2 ms

The RF pulse generator module 106 may be initially programmed to meetthe specific parameter settings for each individual patient during theinitial implantation procedure. Because medical conditions or the bodyitself can change over time, the ability to re-adjust the parametersettings may be beneficial to ensure ongoing efficacy of the neuralmodulation therapy.

The programmer module 102 may be functionally a smart device andassociated application. The smart device hardware may include a CPU 206and be used as a vehicle to handle touchscreen input on a graphical userinterface (GUI) 204, for processing and storing data.

The RF pulse generator module 106 may be connected via wired connection108 to an external TX antenna 110. Alternatively, both the antenna andthe RF pulse generator are located subcutaneously (not shown).

The signals sent by RF pulse generator module 106 to the implantedwireless stimulator device 114 may include both power andparameter-setting attributes in regards to stimulus waveform, amplitude,pulse width, and frequency. The RF pulse generator module 106 can alsofunction as a wireless receiving unit that receives feedback signalsfrom the implanted wireless stimulator device 114. To that end, the RFpulse generator module 106 may contain microelectronics or othercircuitry to handle the generation of the signals transmitted to thedevice 114 as well as handle feedback signals, such as those from thestimulator device 114. For example, the RF pulse generator module 106may comprise controller subsystem 214, high-frequency oscillator 218, RFamplifier 216, a RF switch, and a feedback subsystem 212.

The controller subsystem 214 may include a CPU 230 to handle dataprocessing, a memory subsystem 228 such as a local memory, communicationsubsystem 234 to communicate with programmer module 102 (includingreceiving stimulation parameters from programmer module), pulsegenerator circuitry 236, and digital/analog (D/A) converters 232.

The controller subsystem 214 may be used by the patient and/or theclinician to control the stimulation parameter settings (for example, bycontrolling the parameters of the signal sent from RF pulse generatormodule 106 to the stimulator device 114). These parameter settings canaffect, for example, the power, current level, or shape of the one ormore electrical pulses. The programming of the stimulation parameterscan be performed using the programming module 102, as described above,to set the repetition rate, pulse width, amplitude, and waveform thatwill be transmitted by RF energy to the receiving (RX) antenna 238,typically a dipole antenna (although other types may be used), in theimplanted wireless stimulation device 214. The clinician may have theoption of locking and/or hiding certain settings within the programmerinterface, thus limiting the patient's ability to view or adjust certainparameters because adjustment of certain parameters may require detailedmedical knowledge of neurophysiology, neuroanatomy, protocols for neuralmodulation, and safety limits of electrical stimulation.

The controller subsystem 214 may store received parameter settings inthe local memory subsystem 228, until the parameter settings aremodified by new input data received from the programming module 102. TheCPU 206 may use the parameters stored in the local memory to control thepulse generator circuitry 236 to generate a stimulus waveform that ismodulated by a high frequency oscillator 218 in the range from 300 MHzto 8 GHz (preferably between about 700 MHz and 5.8 GHz and morepreferably between about 800 MHz and 1.3 GHz). The resulting RF signalmay then be amplified by RF amplifier 226 and then sent through an RFswitch 223 to the TX antenna 110 to reach through depths of tissue tothe RX antenna 238.

In some implementations, the RF signal sent by TX antenna 110 may simplybe a power transmission signal used by the wireless stimulation devicemodule 114 to generate electric pulses. In other implementations, atelemetry signal may also be transmitted to the wireless stimulatordevice 114 to send instructions about the various operations of thewireless stimulator device 114. The telemetry signal may be sent by themodulation of the carrier signal (through the skin if external, orthrough other body tissues if the pulse generator module 106 isimplanted subcutaneously). The telemetry signal is used to modulate thecarrier signal (a high frequency signal) that is coupled onto theimplanted antenna(s) 238 and does not interfere with the input receivedon the same stimulator device to power the device. In one embodiment thetelemetry signal and powering signal are combined into one signal, wherethe RF telemetry signal is used to modulate the RF powering signal, andthus the wireless stimulation device is powered directly by the receivedtelemetry signal; separate subsystems in the wireless stimulation deviceharness the power contained in the signal and interpret the data contentof the signal.

The RF switch 223 may be a multipurpose device such as a dualdirectional coupler, which passes the relatively high amplitude,extremely short duration RF pulse to the TX antenna 110 with minimalinsertion loss while simultaneously providing two low-level outputs tofeedback subsystem 212; one output delivers a forward power signal tothe feedback subsystem 212, where the forward power signal is anattenuated version of the RF pulse sent to the TX antenna 110, and theother output delivers a reverse power signal to a different port of thefeedback subsystem 212, where reverse power is an attenuated version ofthe reflected RF energy from the TX Antenna 110.

During the on-cycle time (when an RF signal is being transmitted towireless stimulator device 114), the RF switch 223 is set to send theforward power signal to feedback subsystem. During the off-cycle time(when an RF signal is not being transmitted to the wireless stimulatordevice 114), the RF switch 223 can change to a receiving mode in whichthe reflected RF energy and/or RF signals from the wireless stimulatordevice 114 are received to be analyzed in the feedback subsystem 212.

The feedback subsystem 212 of the RF pulse generator module 106 mayinclude reception circuitry to receive and extract telemetry or otherfeedback signals from the wireless stimulator device 114 and/orreflected RF energy from the signal sent by TX antenna 110. The feedbacksubsystem may include an amplifier 226, a filter 224, a demodulator 222,and an A/D converter 220.

The feedback subsystem 212 receives the forward power signal andconverts this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. In this way thecharacteristics of the generated RF pulse can be compared to a referencesignal within the controller subsystem 214. If a disparity (error)exists in any parameter, the controller subsystem 214 can adjust theoutput to the RF pulse generator 106. The nature of the adjustment canbe, for example, proportional to the computed error. The controllersubsystem 214 can incorporate additional inputs and limits on itsadjustment scheme such as the signal amplitude of the reverse power andany predetermined maximum or minimum values for various pulseparameters.

The reverse power signal can be used to detect fault conditions in theRF-power delivery system. In an ideal condition, when TX antenna 110 hasperfectly matched impedance to the tissue that it contacts, theelectromagnetic waves generated from the RF pulse generator 106 passunimpeded from the TX antenna 110 into the body tissue. However, inreal-world applications a large degree of variability may exist in thebody types of users, types of clothing worn, and positioning of theantenna 110 relative to the body surface. Since the impedance of theantenna 110 depends on the relative permittivity of the underlyingtissue and any intervening materials, and also depends on the overallseparation distance of the antenna from the skin, in any givenapplication there can be an impedance mismatch at the interface of theTX antenna 110 with the body surface. When such a mismatch occurs, theelectromagnetic waves sent from the RF pulse generator 106 are partiallyreflected at this interface, and this reflected energy propagatesbackward through the antenna feed.

The dual directional coupler RF switch 223 may prevent the reflected RFenergy propagating back into the amplifier 226, and may attenuate thisreflected RF signal and send the attenuated signal as the reverse powersignal to the feedback subsystem 212. The feedback subsystem 212 canconvert this high-frequency AC signal to a DC level that can be sampledand sent to the controller subsystem 214. The controller subsystem 214can then calculate the ratio of the amplitude of the reverse powersignal to the amplitude of the forward power signal. The ratio of theamplitude of reverse power signal to the amplitude level of forwardpower may indicate severity of the impedance mismatch.

In order to sense impedance mismatch conditions, the controllersubsystem 214 can measure the reflected-power ratio in real time, andaccording to preset thresholds for this measurement, the controllersubsystem 214 can modify the level of RF power generated by the RF pulsegenerator 106. For example, for a moderate degree of reflected power thecourse of action can be for the controller subsystem 214 to increase theamplitude of RF power sent to the TX antenna 110, as would be needed tocompensate for slightly non-optimum but acceptable TX antenna couplingto the body. For higher ratios of reflected power, the course of actioncan be to prevent operation of the RF pulse generator 106 and set afault code to indicate that the TX antenna 110 has little or no couplingwith the body. This type of reflected-power fault condition can also begenerated by a poor or broken connection to the TX antenna. In eithercase, it may be desirable to stop RF transmission when thereflected-power ratio is above a defined threshold, because internallyreflected power can lead to unwanted heating of internal components, andthis fault condition means the system cannot deliver sufficient power tothe implanted wireless stimulation device and thus cannot delivertherapy to the user.

The controller 242 of the wireless stimulator device 114 may transmitinformational signals, such as a telemetry signal, through the antenna238 to communicate with the RF pulse generator module 106 during itsreceive cycle. For example, the telemetry signal from the wirelessstimulator device 114 may be coupled to the modulated signal on thedipole antenna(s) 238, during the on and off state of the transistorcircuit to enable or disable a waveform that produces the correspondingRF bursts necessary to transmit to the external (or remotely implanted)pulse generator module 106. The antenna(s) 238 may be connected toelectrodes 254 in contact with tissue to provide a return path for thetransmitted signal. An A/D (not shown) converter can be used to transferstored data to a serialized pattern that can be transmitted on thepulse-modulated signal from the internal antenna(s) 238 of the wirelessstimulator device 114.

A telemetry signal from the implanted wireless stimulator device 114 mayinclude stimulus parameters such as the power or the amplitude of thecurrent that is delivered to the tissue from the electrodes. Thefeedback signal can be transmitted to the RF pulse generator module 116to indicate the strength of the stimulus at the nerve bundle by means ofcoupling the signal to the implanted RX antenna 238, which radiates thetelemetry signal to the external (or remotely implanted) RF pulsegenerator module 106. The feedback signal can include either or both ananalog and digital telemetry pulse modulated carrier signal. Data suchas stimulation pulse parameters and measured characteristics ofstimulator performance can be stored in an internal memory device withinthe implanted stimulator device 114, and sent on the telemetry signal.The frequency of the carrier signal may be in the range of at 300 MHz to8 GHz (preferably between about 700 MHz and 5.8 GHz and more preferablybetween about 800 MHz and 1.3 GHz).

In the feedback subsystem 212, the telemetry signal can be downmodulated using demodulator 222 and digitized by being processed throughan analog to digital (A/D) converter 220. The digital telemetry signalmay then be routed to a CPU 230 with embedded code, with the option toreprogram, to translate the signal into a corresponding currentmeasurement in the tissue based on the amplitude of the received signal.The CPU 230 of the controller subsystem 214 can compare the reportedstimulus parameters to those held in local memory 228 to verify thewireless stimulator device 114 delivered the specified stimuli totissue. For example, if the wireless stimulation device reports a lowercurrent than was specified, the power level from the RF pulse generatormodule 106 can be increased so that the implanted wireless stimulatordevice 114 will have more available power for stimulation. The implantedwireless stimulator device 114 can generate telemetry data in real time,for example, at a rate of 8 Kbits per second. All feedback data receivedfrom the implanted stimulator device 114 can be logged against time andsampled to be stored for retrieval to a remote monitoring systemaccessible by the health care professional for trending and statisticalcorrelations.

The sequence of remotely programmable RF signals received by theinternal antenna(s) 238 may be conditioned into waveforms that arecontrolled within the implantable wireless stimulator device 114 by thecontrol subsystem 242 and routed to the appropriate electrodes 254 thatare placed in proximity to the tissue to be stimulated. For instance,the RF signal transmitted from the RF pulse generator module 106 may bereceived by RX antenna 238 and processed by circuitry, such as waveformconditioning circuitry 240, within the implanted wireless stimulatordevice 114 to be converted into electrical pulses applied to theelectrodes 254 through electrode interface 252. In some implementations,the implanted wireless stimulator device 114 contains between two tosixteen electrodes 254.

The waveform conditioning circuitry 240 may include a rectifier 244,which rectifies the signal received by the RX antenna 238. The rectifiedsignal may be fed to the controller 242 for receiving encodedinstructions from the RF pulse generator module 106. The rectifiersignal may also be fed to a charge balance component 246 that isconfigured to create one or more electrical pulses based such that theone or more electrical pulses result in a substantially zero net chargeat the one or more electrodes (that is, the pulses are charge balanced).The charge-balanced pulses are passed through the current limiter 248 tothe electrode interface 252, which applies the pulses to the electrodes254 as appropriate.

The current limiter 248 insures the current level of the pulses appliedto the electrodes 254 is not above a threshold current level. In someimplementations, an amplitude (for example, current level, voltagelevel, or power level) of the received RF pulse directly determines theamplitude of the stimulus. In this case, it may be particularlybeneficial to include current limiter 248 to prevent excessive currentor charge being delivered through the electrodes, although currentlimiter 248 may be used in other implementations where this is not thecase. Generally, for a given electrode having several square millimeterssurface area, it is the charge per phase that should be limited forsafety (where the charge delivered by a stimulus phase is the integralof the current). But, in some cases, the limit can instead be placed onthe current, where the maximum current multiplied by the maximumpossible pulse duration is less than or equal to the maximum safecharge. More generally, the limiter 248 acts as a charge limiter thatlimits a characteristic (for example, current or duration) of theelectrical pulses so that the charge per phase remains below a thresholdlevel (typically, a safe-charge limit).

In the event the implanted wireless stimulator device 114 receives a“strong” pulse of RF power sufficient to generate a stimulus that wouldexceed the predetermined safe-charge limit, the current limiter 248 canautomatically limit or “clip” the stimulus phase to maintain the totalcharge of the phase within the safety limit. The current limiter 248 maybe a passive current limiting component that cuts the signal to theelectrodes 254 once the safe current limit (the threshold current level)is reached. Alternatively, or additionally, the current limiter 248 maycommunicate with the electrode interface 252 to turn off all electrodes254 to prevent tissue damaging current levels.

A clipping event may trigger a current limiter feedback control mode.The action of clipping may cause the controller to send a thresholdpower data signal to the pulse generator 106. The feedback subsystem 212detects the threshold power signal and demodulates the signal into datathat is communicated to the controller subsystem 214. The controllersubsystem 214 algorithms may act on this current-limiting condition byspecifically reducing the RF power generated by the RF pulse generator,or cutting the power completely. In this way, the pulse generator 106can reduce the RF power delivered to the body if the implanted wirelessstimulator device 114 reports it is receiving excess RF power.

The controller 250 of the stimulator 205 may communicate with theelectrode interface 252 to control various aspects of the electrodesetup and pulses applied to the electrodes 254. The electrode interface252 may act as a multiplex and control the polarity and switching ofeach of the electrodes 254. For instance, in some implementations, thewireless stimulator 106 has multiple electrodes 254 in contact withtissue, and for a given stimulus the RF pulse generator module 106 canarbitrarily assign one or more electrodes to 1) act as a stimulatingelectrode, 2) act as a return electrode, or 3) be inactive bycommunication of assignment sent wirelessly with the parameterinstructions, which the controller 250 uses to set electrode interface252 as appropriate. It may be physiologically advantageous to assign,for example, one or two electrodes as stimulating electrodes and toassign all remaining electrodes as return electrodes.

Also, in some implementations, for a given stimulus pulse, thecontroller 250 may control the electrode interface 252 to divide thecurrent arbitrarily (or according to instructions from pulse generatormodule 106) among the designated stimulating electrodes. This controlover electrode assignment and current control can be advantageousbecause in practice the electrodes 254 may be spatially distributedalong various neural structures, and through strategic selection of thestimulating electrode location and the proportion of current specifiedfor each location, the aggregate current distribution in tissue can bemodified to selectively activate specific neural targets. This strategyof current steering can improve the therapeutic effect for the patient.

In another implementation, the time course of stimuli may be arbitrarilymanipulated. A given stimulus waveform may be initiated at a timeT_start and terminated at a time T_final, and this time course may besynchronized across all stimulating and return electrodes; further, thefrequency of repetition of this stimulus cycle may be synchronous forall the electrodes. However, controller 250, on its own or in responseto instructions from pulse generator 106, can control electrodeinterface 252 to designate one or more subsets of electrodes to deliverstimulus waveforms with non-synchronous start and stop times, and thefrequency of repetition of each stimulus cycle can be arbitrarily andindependently specified.

For example, a stimulator having eight electrodes may be configured tohave a subset of five electrodes, called set A, and a subset of threeelectrodes, called set B. Set A might be configured to use two of itselectrodes as stimulating electrodes, with the remainder being returnelectrodes. Set B might be configured to have just one stimulatingelectrode. The controller 250 could then specify that set A deliver astimulus phase with 3 mA current for a duration of 200 us followed by a400 us charge-balancing phase. This stimulus cycle could be specified torepeat at a rate of 60 cycles per second. Then, for set B, thecontroller 250 could specify a stimulus phase with 1 mA current forduration of 500 us followed by a 800 us charge-balancing phase. Therepetition rate for the set-B stimulus cycle can be set independently ofset A, say for example it could be specified at 25 cycles per second.Or, if the controller 250 was configured to match the repetition ratefor set B to that of set A, for such a case the controller 250 canspecify the relative start times of the stimulus cycles to be coincidentin time or to be arbitrarily offset from one another by some delayinterval.

In some implementations, the controller 250 can arbitrarily shape thestimulus waveform amplitude, and may do so in response to instructionsfrom pulse generator 106. The stimulus phase may be delivered by aconstant-current source or a constant-voltage source, and this type ofcontrol may generate characteristic waveforms that are static, e.g. aconstant-current source generates a characteristic rectangular pulse inwhich the current waveform has a very steep rise, a constant amplitudefor the duration of the stimulus, and then a very steep return tobaseline. Alternatively, or additionally, the controller 250 canincrease or decrease the level of current at any time during thestimulus phase and/or during the charge-balancing phase. Thus, in someimplementations, the controller 250 can deliver arbitrarily shapedstimulus waveforms such as a triangular pulse, sinusoidal pulse, orGaussian pulse for example. Similarly, the charge-balancing phase can bearbitrarily amplitude-shaped, and similarly a leading anodic pulse(prior to the stimulus phase) may also be amplitude-shaped.

As described above, the wireless stimulator device 114 may include acharge-balancing component 246. Generally, for constant currentstimulation pulses, pulses should be charge balanced by having theamount of cathodic current should equal the amount of anodic current,which is typically called biphasic stimulation. Charge density is theamount of current times the duration it is applied, and is typicallyexpressed in the units uC/cm². In order to avoid the irreversibleelectrochemical reactions such as pH change, electrode dissolution aswell as tissue destruction, no net charge should appear at theelectrode-electrolyte interface, and it is generally acceptable to havea charge density less than 30 uC/cm². Biphasic stimulating currentpulses ensure that no net charge appears at the electrode after eachstimulation cycle and the electrochemical processes are balanced toprevent net dc currents. The wireless stimulator device 114 may bedesigned to ensure that the resulting stimulus waveform has a net zerocharge. Charge balanced stimuli are thought to have minimal damagingeffects on tissue by reducing or eliminating electrochemical reactionproducts created at the electrode-tissue interface.

A stimulus pulse may have a negative-voltage or current, called thecathodic phase of the waveform. Stimulating electrodes may have bothcathodic and anodic phases at different times during the stimulus cycle.An electrode that delivers a negative current with sufficient amplitudeto stimulate adjacent neural tissue is called a “stimulating electrode.”During the stimulus phase the stimulating electrode acts as a currentsink. One or more additional electrodes act as a current source andthese electrodes are called “return electrodes.” Return electrodes areplaced elsewhere in the tissue at some distance from the stimulatingelectrodes. When a typical negative stimulus phase is delivered totissue at the stimulating electrode, the return electrode has a positivestimulus phase. During the subsequent charge-balancing phase, thepolarities of each electrode are reversed.

In some implementations, the charge balance component 246 uses ablocking capacitor(s) placed electrically in series with the stimulatingelectrodes and body tissue, between the point of stimulus generationwithin the stimulator circuitry and the point of stimulus delivery totissue. In this manner, a resistor-capacitor (RC) network may be formed.In a multi-electrode stimulator, one charge-balance capacitor(s) may beused for each electrode or a centralized capacitor(s) may be used withinthe stimulator circuitry prior to the point of electrode selection. TheRC network can block direct current (DC), however it can also preventlow-frequency alternating current (AC) from passing to the tissue. Thefrequency below which the series RC network essentially blocks signalsis commonly referred to as the cutoff frequency, and in one embodimentthe design of the stimulator system may ensure the cutoff frequency isnot above the fundamental frequency of the stimulus waveform. In thisembodiment as disclosed herein, the wireless stimulator may have acharge-balance capacitor with a value chosen according to the measuredseries resistance of the electrodes and the tissue environment in whichthe stimulator is implanted. By selecting a specific capacitance valuethe cutoff frequency of the RC network in this embodiment is at or belowthe fundamental frequency of the stimulus pulse.

In other implementations, the cutoff frequency may be chosen to be at orabove the fundamental frequency of the stimulus, and in this scenariothe stimulus waveform created prior to the charge-balance capacitor,called the drive waveform, may be designed to be non-stationary, wherethe envelope of the drive waveform is varied during the duration of thedrive pulse. For example, in one embodiment, the initial amplitude ofthe drive waveform is set at an initial amplitude Vi, and the amplitudeis increased during the duration of the pulse until it reaches a finalvalue k*Vi. By changing the amplitude of the drive waveform over time,the shape of the stimulus waveform passed through the charge-balancecapacitor is also modified. The shape of the stimulus waveform may bemodified in this fashion to create a physiologically advantageousstimulus.

In some implementations, the wireless stimulator device 114 may create adrive-waveform envelope that follows the envelope of the RF pulsereceived by the receiving dipole antenna(s) 238. In this case, the RFpulse generator module 106 can directly control the envelope of thedrive waveform within the wireless stimulator device 114, and thus noenergy storage may be required inside the stimulator itself. In thisimplementation, the stimulator circuitry may modify the envelope of thedrive waveform or may pass it directly to the charge-balance capacitorand/or electrode-selection stage.

In some implementations, the implanted wireless stimulator device 114may deliver a single-phase drive waveform to the charge balancecapacitor or it may deliver multiphase drive waveforms. In the case of asingle-phase drive waveform, for example, a negative-going rectangularpulse, this pulse comprises the physiological stimulus phase, and thecharge-balance capacitor is polarized (charged) during this phase. Afterthe drive pulse is completed, the charge balancing function is performedsolely by the passive discharge of the charge-balance capacitor, whereis dissipates its charge through the tissue in an opposite polarityrelative to the preceding stimulus. In one implementation, a resistorwithin the stimulator facilitates the discharge of the charge-balancecapacitor. In some implementations, using a passive discharge phase, thecapacitor may allow virtually complete discharge prior to the onset ofthe subsequent stimulus pulse.

In the case of multiphase drive waveforms the wireless stimulator mayperform internal switching to pass negative-going or positive-goingpulses (phases) to the charge-balance capacitor. These pulses may bedelivered in any sequence and with varying amplitudes and waveformshapes to achieve a desired physiological effect. For example, thestimulus phase may be followed by an actively driven charge-balancingphase, and/or the stimulus phase may be preceded by an opposite phase.Preceding the stimulus with an opposite-polarity phase, for example, canhave the advantage of reducing the amplitude of the stimulus phaserequired to excite tissue.

In some implementations, the amplitude and timing of stimulus andcharge-balancing phases is controlled by the amplitude and timing of RFpulses from the RF pulse generator module 106, and in others thiscontrol may be administered internally by circuitry onboard the wirelessstimulator device 114, such as controller 250. In the case of onboardcontrol, the amplitude and timing may be specified or modified by datacommands delivered from the pulse generator module 106.

In some applications, the transmit antenna 110 can be placed in closeproximity to the receiving antenna 238. For example, the transmitantenna 110 may be worn by the patient. In other examples, the transmitantenna 110 may be placed further away from the patient (and theimplanted passive neural stimulator that houses receiving antenna 238).In the former case, less energy may be emitted from the remote antennato wirelessly provide power and stimulation parameter settings to thepassive neural stimulator. In some scenarios, the patient may remainstationary or asleep. During sleep, the patient may not desire to wear atransmitting antenna 110 that is coupled to a controller module (such ascontroller subsystem 214) through a cable. An antenna assembly may beused to remotely provide power and stimulation parameter settings to thepassive neural stimulator. The antenna assembly in this example may bemore than 10 centimeters away from the passive neural stimulatorimplanted inside a patient. If the patient can move around a room; theentire room may need to be illuminated with the microwave energy field.In this scenario, an array of antennas, or a broad beam-width antenna,may be used. Some implementations may incorporate a steerable (e.g.,mechanically, electrically) arrangement of antennas that include areceiving antenna location tracking system. These implementations mayfurther apply motion control of the transmitting antenna 110 to adjustangle or orientation of illumination of an antenna to point in thedirection of the receiving antenna. The output power is adjusted asneeded depending on the distance between the transmitting and receivingantennas and the directivity of the transmitting antenna.

FIGS. 3A-3C show examples of operations of a RF stimulation system.These examples may incorporate a single remote transmitting antenna oran array of transmitting antennas. In some instances, the array may besteerable to focus on a particular location. In other instances, thetransmitting antenna(s) may be fixed.

In FIG. 3A, a patient 304 implanted with a neural stimulator device 114is resting in bed 306 while receiving therapy from a transmittingantenna system 302 (e.g., transmitting antenna 110 and controllersubsystem 214). As illustrated, the transmitting antenna system 302 isplaced elsewhere in the same room to transmit electromagnetic energy 308including power and stimulation parameters to implanted neuralstimulator device 114. For example, the remote transmitting antennasystem 302 may be placed on a dresser 310 or a night-stand near thepatient bed. The remote transmitting antenna 310 system may be batteryor wall powered. The remote transmitting antenna system 310 may receiveprogramming or therapeutic instructions manually via physical buttons(or other tactile user interface on controller subsystem 214) or by awireless instruction protocol such as Bluetooth or RF (e.g., cellular,Wi-Fi, etc.) from a programming module (not shown). The patient 304 maycontrol the remote transmitting antenna system 302 via the physicalbuttons or Bluetooth.

FIG. 3B depicts a similar scenario of transmitting electromagneticenergy 308 to remotely provide power and stimulator parameters to animplanted neural stimulator device 114 while patient 304 is standing orwalking around without a wearable antenna system. In this illustration,transmitting antenna system 302 (e.g., transmitting antenna 110 andcontroller subsystem 214) is placed on arbitrary furniture 320 in thesame room as the standing or walking patient.

FIG. 3C depicts another similar scenario in which patient 304 withimplanted neural stimulator device 114 is sitting away from transmittingantenna system 302 (e.g., transmitting antenna 110 and controllersubsystem 214). For example, patient 304 may sit in an office chair. Inthis illustration, electromagnetic energy 308 is transmitted fromtransmitting antenna system 302 to remotely provide power andstimulation parameters to an implanted neural stimulator device 114.

FIG. 4A illustrates a top view of radiation volume 404 as transmittedfrom the remote transmitting antenna system 302. More particularly, therange of the remote transmitting antenna system 302 is shown asgenerally conical and directional, extending in one direction from theremote transmitting antenna system 302. Generally, the patient 406 mayneed to stay within the radiation volume to receive the desiredstimulation therapy. The volume may interact with a standing or sittingpatient (i.e., the remote transmitting antenna system may be configuredto interact with an implanted antenna within a given distance andeffective angle from the remote antenna).

FIG. 4B illustrates a side and three-dimensional view of radiationvolume 404 as generated by the remote transmitting antenna system 302.In this illustration, the system radiation volume 404 can cover apatient 406 standing within the effective angles/distances to generatean effective electric field at the receiving antenna on implanted neuralstimulator device 114 while the patient is standing.

In these illustrations, wireless transmission of power and stimulationparameters generally operate by line of sight. In other words,transmitting antenna system 302 generally emits electromagneticradiation through free space and then into the human body and implantedneural stimulator device 114. Blocking objects, such as those with lossyconducting material (e.g., low permittivity) or a material that reflectsRF, such as metals, may negatively impact wireless transmission.

In these illustrations, the position of transmitting antenna system 302may be adjusted such that a radiating surface of transmitting antennasystem 302 is no less than one foot from the implanted neural stimulatordevice. In this configuration, transmitting antenna system 302 may notbe a wearable gear for the patient. The position of transmitting antennasystem 302 may also be adjusted such that the radiating surface oftransmitting antenna system 302 is no more than six foot from theimplanted neural stimulator device in order for the implantable neuralstimulator device to receive sufficient operating energy wirelessly fromthe transmitting antenna system 302. Transmitting antenna system 302 mayradiate polarized electromagnetic energy and an orientation of atransmitting antenna on the transmitting antenna system 302 may beadjusted so that the transmitting antenna is better aligned with thereceiving antenna on the implantable neural stimulator device. When thealignment is improved through re-orientation, electromagnetic energyreceived at the receiving antenna can be increased as well.

Referring generally to FIGS. 5A-5B, the general design of the UWBantenna (i.e., for the remote transmitting antenna system 302) is shown.As illustrated, remote transmitting antenna system 302 includes arectangular aperture waveguide 506 surrounding the antenna having aradiating surface 504 and a feed port 502. Feed port 502 may include acable connector 508 for coupling to a cable. Example connectors mayinclude BNC (Bayonet Neill-Concelman) connector, or SMA (SubMiniatureversion A) connectors.

In this example, the radiating surface 504 of the antenna isbowtie-shaped. In addition to two leaf structures 504C1 and 504C2, thisbowtie shape also includes two rod structures 504A and 504B connectingthe two leaf structures. The bowtie-shaped radiating surface 504 hascontacts 504C and 504D connecting wave guide 506. The bowtie antennadistributes electromagnetic field in wave guide 506 and induces waveguide mode of propagation polarized along, for example, a long axis ofrod structures 504A and 504B. The bowtie antenna may radiate over a widebandwidth like a dipole. Surrounding the antenna with waveguide 506improves directivity of the antenna. Scaling the antenna size candetermine the bandwidth of the antenna. In one implementation, theantenna size may be scaled such that the antenna is parameterized tohave a band from 500 MHz to 4 GHz. The scaling may be simplified to justthe length, width, and height of the interior of the rectangularwaveguide.

One example of optimized dimensions of the antenna are presented inTable 1 below:

TABLE 1 UWB Antenna example dimensions following parameterizationOptimized UWB Antenna Dimension Value [units] Length of the Waveguide(Interior)   30 [cm] Width of the Waveguide (Interior)   15 [cm] Heightof the Waveguide (Interior) 10.03 [cm]The waveguide dimensions may be scaled with the operating frequency ofthe bowtie-shaped antenna. For context, each wave guide has a cut-offfrequency beyond which the wave guide cannot support wave propagation.When a wave guide surrounds a transmitting antenna, for example thebowtie shaped antenna as illustrated, the wave guide needs to be largeenough to support the propagation of the electromagnetic wave from thetransmitting antenna. Yet, it is advantageous to have a compacttransmitting antenna system for applications as depicted in FIGS. 3A-3C.

The bowtie antenna assembly as depicted herein may be smaller in sizethan horn antennas operating at the same frequency. In some instances,bowtie antenna assembly can be a factor of 2 to 3 smaller than a hornantenna operating at the same frequency. In addition to a reduction ofthe waveguide cross-section and total length, the directivity of thebowtie antenna assembly may also be controlled. In some instances, theantenna may include a tapered dielectric transition from the mouth ofthe waveguide and over the radiating surface. The tapering may match thewaveguide at the mouth so that the reflection back to the feed port 508is reduced. The tapering may also focus the main beam of the bowtieantenna by spatially narrowing the beam width. For example, tapering inone spatial dimension can lead to narrowing of the beam width of thetransmitted electromagnetic beam in the same dimension.

The design for an ultra-wide band (UWB) antenna is shown below, withanalysis through modeling. Strong correlation is demonstrated betweenthe theoretical results and the actual measured results from aprototype, thereby verifying the accuracy and validity of the simulationmodel. Generally, cavity backed rectangular aperture antennas (CB-RAA,as used herein) have performance characteristics that lend themselveswell to the remote antenna application. CB-RAA can possess radiationcharacteristics for radiating over a wide bandwidth. Further, itsradiation efficiency is very close to that from a circular aperture (81%vs. 83.6%), while the electric field lines of CB-RAA are parallel,thereby improving the cross-polarization performance when thetransmission is off the bore sight of the transmitting antenna 110.

These features for the UWB antenna may be incorporated into thetransmitting antenna 110 discussed herein. The remote transmittingantenna 110 is advantageously a directional, efficient, and far reachingantenna, all while relatively simple and easy to manufacture. Thecross-polarization and E-field orientation for the transmitting antenna110 may allow for a range of positions for placing the antenna such thatsufficient energy reaches the implanted antenna to power the same. Thelarge bandwidth response associated with addition of the waveguide andfocusing lens may allow fine-tuning of the transmitting antenna 110 to aparticular frequency, thereby rendering antenna more capable to operateat various particular frequencies.

Referring to FIGS. 6A-6C, an example of an antenna assembly with a waveguide are shown. In FIGS. 6A-6B, a side plate is removed to reveal theinternal structure of the antenna assembly, which includes thetransmitting antenna 110 with a bowtie-shaped radiating surface and afeed port coupled to a cable connector. FIG. 6C depicts an intactantenna assembly (with no sidewalls removed). The dimensions match thedimensions of the target antenna model (shown in Table 1) within atolerance of ±0.5 mm.

FIG. 7 illustrates the comparison of return loss over the frequency bandof interest for the HFSS model (from the finite element solver) and theprototype of the antenna assembly of FIG. 6. The return losscharacterizes the amount of reflected energy from impedance mismatchingof the antenna. More reflection loss indicates a more effective powertransfer. As shown in FIG. 7, both simulated and actually measuredvalues for the return loss were generally less than or equal to −5 dB.The actually measured prototype values closely matched or improved uponthe modeling results at frequencies between 500 MHz and 1.25 GHz.

FIG. 8 shows an example of simulated return loss characteristics of anantenna assembly designed with a resonance frequency of 915 MHz. Asshown, a reflection notch occurs at 915 MHz as desired following theparameterizing of the bowtie antenna to 915 MHz.

FIGS. 9A-9B show examples of simulated electromagnetic radiationpatterns from the antenna assembly of FIG. 8. These patterns correspondto the total far field radiation pattern at resonance (915 MHz) for theparameterized bowtie antenna. In FIG. 9A, the pattern is calculated forthe bowtie antenna and without a wave guide. In this arrangement, thebowtie antenna radiates uniformly around its axis of polarization. Toimprove directivity of the transmitting antenna 110, a rectangularwaveguide can be placed around the bowtie antenna. FIG. 9B shows theimproved directivity as demonstrated in the far field radiation patternfor the bowtie antenna at resonance (915 MHz) and with a rectangularaperture waveguide. As illustrated, the energy is concentrated in a lobeas directed by the aperture of the waveguide. Thus, adding the waveguidearound the bowtie antenna significantly increases the antennadirectivity as desired. In some cases, the beam width can be reduced by50% or more by the rectangular waveguide. However, the return loss, andin turn the impedance match, may decrease due to frequency shapingcaused by a cutoff frequency of the wave guide. To mitigate this downside, the mouth of the waveguide may be loaded with a tapered dielectric(e.g., Dk=3) dome.

Referring now to FIG. 10, a dielectric dome 1006 is mounted on the mouthof the waveguide aperture 1004 and over the radiating surface 1002. Inthis arrangement, the dome 1004 acts as a focusing lens at the mouth ofthe antenna. The addition of the dielectric dome 1006 to fill the waveguide and over the mouth of the wave guide can provide several benefitsto the design of the bowtie antenna, including, for example, loweringthe return loss cutoff frequency of the rectangular wave guide withoutthe dielectric filling to below 915 MHz so that the size of therectangular wave guide can be further reduced. Further, the dielectricdome, when tapered, can spatially narrow the energy transmitted so thatthe transmission becomes more focused. For example, the dielectric dome,tapered in one dimension, can cause the beam width of the radiatedelectromagnetic wave to be narrower in the same dimension.

The dome may be of a simple half-cycle sinusoid or Gaussian shape, forexample, along the Y direction (while the profile along the X-directionmay remain constant). As discussed above, the antenna assembly mayinduce a wave guide mode of transmission pattern that is polarized alongthe X direction (along the direction of the long axis of rod structures1002A and 1002B). Notably, the shaped dielectric dome may fill the waveguide above and below the bowtie antenna. Yet, the shape or profilevariation extends only from the mouth of the wave guide, as illustrated.The shape or profile variation—along the Y direction as illustrated inthis case—may facilitate reducing the spread of the transmittedelectromagnetic energy as it propagates forward.

The height of the dome—Hdome—can be configured to improve S11 (returnloss) and S21 (transmission loss). The height of dome refers to theheight extending from the month of the wave guide to the summit of thedome. In some implementations, the height may vary from 0.5 in to 6 in,depending on the dielectric constant, which can vary from 1.5 to 9. Fora 915 MHz operation, the height of the dielectric dome was chosen at 3inches.

As illustrated, L denotes the length of the wave guide and scales in therange from 2.5 cm to 10 cm. Hbowtie refers to the height position of theBowtie and may be fixed at L/2. In this illustration, “a” refers to theshorter lateral dimension of wave guide base, which can scale in therange from 3.75 cm to 7.5 cm, while “b” refers to the longer lateraldimension of the wave guide base, which may range from 7.5 cm to 15 cm.Choosing a particular dielectric constant may reduce the size of thewave guide. The dielectric constant may also help release theelectromagnetic wave from the metal wave guide, thereby serving as abuffer to reduce the reflection at the feed port. The feed port may becoupled to a 50 ohm coaxial cable via various connectors (e.g., BNC,SMA, etc.) as discussed above.

FIGS. 11A-11B shows the simulated return loss and transmissioncharacteristics of the antenna assembly of FIG. 10. In FIG. 11A, thereturn loss is plotted as a function of frequency, for a range of domeheights. In particular, the return loss shown is a relative return loss,as compared to a baseline return loss for two dipole antennas operatingat 915 MHz and separated at 1 in apart. The results from theparameterizations (i.e., designing by adjusting system parameters) showthat a dome height of three inches and greater produce good matches.However, the size trade-offs for the relatively small gains inreflection loss indicate only marginal gains above three inches. Thus,three inches may be deemed as the smallest height with an acceptablereflection loss, and thus the desirable dome height.

FIG. 11B shows the simulated transmission loss versus frequency for arange of dome heights. Transmission loss is a characterization of theattenuation of the transmitted electromagnetic wave. Larger values (lessnegative values) correspond to a better transmission loss and a moreefficient antenna. Gains in transmission loss are diminishing when thedome height is over three inches. Notably, the transmission loss mayserve as a complimentary measure of the performance of the remotetransmission antenna. Thus, little benefit may be derived from makingthe dome height larger than three inches.

Following this parameterization, the dimensions can be judiciouslydetermined. An example of dimensions for 915 MHz are presented in Table2. The reflection and transmission loss plots illustrate that the designis substantially improved for the purpose of this disclosure, but tofurther validate the results, the contours of the electric fieldinteractions at the receiver and the far field radiation pattern can beexamined. The waveguide dimensions shown below in Table 2 scale with thedimensions of the bowtie antenna (as shown above in Table 1).

TABLE 2 Final remote antenna dimensions following parameterizationOptimized Remote Antenna Dimension Value [units] Length of the Waveguide(Interior) 15.0 [cm] Width of the Waveguide (Interior)  7.6 [cm] Heightof the Waveguide (Interior)  5.0 [cm]

FIG. 12 shows the perspective view of the simulated electromagneticradiation pattern from the antenna assembly of FIG. 10. In particular,FIG. 12 shows the far field radiation pattern at 915 MHz for the remoteantenna design according to Table 2. The dielectrically loaded waveguidefurther improves directivity of the antenna to provide sufficient energyfor delivery to the implanted neural stimulator device. The far fieldpattern shows that the additional dielectric loading further improvesdirectivity that validates the previously found loss characterizationsas well as the E-field propagation results. Additionally, the patternquantifies the spatial orientation variability of the antenna withrespect to the implanted neural stimulator device. The resultsdemonstrate that the implanted neural stimulator can be within 15° ofthe center axis of the remote transmitting antenna and still receive themajority of the transmitted energy.

FIG. 13A-13B shows the X-Z and Y-Z plane views of the simulatedelectromagnetic radiation pattern of FIG. 12. The receiver antenna 1304is in the top portion of both planes. The contours show a forwardtraveling lobe of electromagnetic energy interacting with the receiverantenna 1304. These graphs show that the transmitting antenna 1302 andthe receiver antenna 1304 couple together well because the transmittingantenna 1302 is directive to the implant that includes receiver antenna1304, and that energy is efficiently delivered to the implant. The farfield radiation pattern at 915 MHz improves due to the furtherparameterizations performed, as discussed above.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherimplementations are within the scope of the following claims.

What is claimed is:
 1. An antenna assembly, comprising: an antenna thatincludes: a metal signal layer having a radiating surface; and a feedport; and a waveguide surrounding the antenna and configured to guideelectromagnetic energy transmitted from the radiating surface in adirection away from the antenna; and a controller module connected tothe feed port and configured to drive the antenna to transmitelectromagnetic energy from the radiating surface; wherein the antenna,waveguide, and controller module are configured such that, when thecontroller module drives the antenna, the transmitted electromagneticenergy matches a reception characteristic of an implantable device andis sufficient for the implantable device to create one or moreelectrical pulses of sufficient amplitude to stimulate neural tissue ofa patient, solely using electromagnetic energy received from theantenna, when the implantable device is located at least 10 centimetersaway from the antenna.
 2. The antenna of claim 1, wherein the radiatingsurface is bowtie shaped and has two leaf structures connecting to eachother at the feed port as well as through two substantially parallel rodstructures.
 3. The antenna assembly of claim 1, further comprising: adielectric lens that fills the wave guide and protrude outward from anopening of the wave guide to form a protrusion that is shaped tospatially narrow the transmitted electromagnetic energy in the directionaway from the transmitting surface.
 4. The antenna assembly of claim 3,wherein the protrusion is tapered in shape.
 5. The antenna assembly ofclaim 4, wherein the protrusion is tapered to have a Gaussian orsinusoid profile.
 6. The antenna assembly of claim 4, wherein theantenna assembly has a return loss cutoff frequency associated with thewave guide and the dielectric lens is further configured to lower thereturn loss cutoff frequency.
 7. The antenna assembly of claim 1,wherein the antenna is operable within a frequency band from about 500MHz to about 4 GHz.
 8. The antenna assembly of claim 2, wherein thetransmitted electromagnetic energy is polarized along a long axis of therod structures.
 9. The antenna assembly of claim 1, wherein theradiating surface is adjustable from a first spatial orientation to asecond spatial orientation such that polarized electromagnetic energyreceived at the implantable device is increased.
 10. The antennaassembly of claim 1, wherein the waveguide is a rectangular waveguidehaving four walls that surround the bowtie shaped radiating surface. 11.The antenna assembly of claim 10, wherein the rectangular waveguide hasan interior length of about 15 cm, an interior width of about 7.6 cm,and a height of about 5 cm.
 12. The antenna assembly of claim 10,wherein the rectangular waveguide has an interior length of at least 10cm, and the rectangular waveguide has an interior length, width, andheight ratio of about 15:7.6:5.
 13. A method for wirelessly supplyingenergy to an implantable device, the method comprising: radiatingelectromagnetic energy from a radiating surface on an antenna assembly,the radiated electromagnetic energy reaching an implantable devicelocated at least 10 centimeters away and implanted inside a patient suchthat the implantable device creates, solely by using the radiatedelectromagnetic energy, one or more electrical stimulation pulsessuitable for stimulating neural tissue of the patient, and applies theelectrical stimulation pulses to neural tissue of the patient, whereinthe radiating surface is bowtie shaped and has two leaf structuresconnecting to each other at the feed port as well as through twosubstantially parallel rod structures.
 14. The method of claim 13,wherein radiating the electromagnetic energy further comprises radiatingthe electromagnetic energy while the patient is asleep such that thecreated one or more electrical simulation pulses is applied to stimulatethe patient's neural tissue during the patient's sleep.
 15. The methodof claim 13, further comprising: adjusting a position of the antennaassembly such that the radiating surface of the antenna assembly is nomore than six feet from the implantable device.
 16. The method of claim13, further comprising: adjusting a position of the antenna assemblysuch that the radiating surface of the antenna assembly is no less thanone foot from the implantable device.
 17. The method of claim 13,further comprising: adjusting an orientation of the antenna assemblysuch that the radiated electromagnetic energy received at theimplantable device is increased.
 18. The method of claim 13, furthercomprising: connecting the antenna assembly to a controller module; anddriving the antenna assembly from the controller module connectedthereto such that the radiating surface on the antenna assembly radiateselectromagnetic energy to power the implantable.
 19. The method of claim18, further comprising: establishing a link between a programming moduleto the controller module; and transmitting, from the programming moduleto the controller module, data encoding parameters of the one or morestimulation pulses to be created at the implantable device and to besubsequently applied to stimulate the patient's neural tissue.
 20. Asystem, comprising: an antenna assembly that wirelessly powers animplantable device, the antenna assembly including: an antenna thatincludes: a metal signal layer having a radiating surface and configuredto transmit electromagnetic energy via radiative coupling; a waveguidesurrounding the antenna and configured to guide electromagnetic energytransmitted from the radiating surface in a direction away from theantenna; and; a controller module connected to the feed port of theantenna and configured to drive the antenna assembly such that theradiating surface on the antenna radiates electromagnetic energy thatmatches a reception characteristic of an implantable device and issufficient for the implantable device to create one or more electricalpulses of sufficient amplitude to stimulate neural tissue of a patient,solely using electromagnetic energy received from the antenna, when theimplantable device is located at least 10 centimeters away from theantenna.
 21. The system fop claim 20, wherein the radiating surface isbowtie shaped and has two leaf structures connecting to each other atthe feed port as well as through two substantially parallel rodstructures.
 22. The system of 20, further comprising: an implantableoperable from a location inside a patient and more than 10 centimetersaway from the antenna assembly, wherein the implantable device createsone or more stimulation pulses of sufficient amplitude to stimulateneural tissue of the patient solely using electromagnetic energyreceived from the antenna assembly.
 23. The system of claim 20, whereinthe waveguide is a rectangular waveguide having four walls that surroundthe radiating surface.
 24. The system of claim 22, wherein therectangular waveguide has an interior length of about 15 cm, an interiorwidth of about 7.6 cm, and a height of about 5 cm.
 25. The system ofclaim 22, wherein the rectangular waveguide has an interior length of atleast 10 cm, and the rectangular waveguide has an interior length,width, and height ratio of about 15:7.6:5.
 26. The system of claim 20,further comprising: a dielectric lens that fills the wave guide andprotrude outward from an opening of the wave guide to form a protrusionthat is shaped to spatially narrow the transmitted electromagneticenergy in the direction away from the transmitting surface.
 27. Thesystem of claim 26, wherein the protrusion is tapered in shape.
 28. Thesystem of claim 27, wherein the protrusion is tapered to have a Gaussianor sinusoid profile.
 29. The system of claim 20, wherein the antenna isoperable within a frequency band from about 500 MHz to about 4 GHz. 30.The system of claim 20, wherein the transmitted electromagnetic energyis polarized along a long axis of the rod structures.
 31. The system ofclaim 20, wherein the implantable device includes a dipole antennalocated on the implantable device inside the patient, and the radiatingsurface is adjustable from a first spatial orientation to a secondspatial orientation such that polarized electromagnetic energy receivedat the dipole antenna is increased.